CN111394402A - Method for co-producing medium-chain fatty acid and biogas by using wood fiber raw material - Google Patents

Abstract

The invention provides a method for co-producing medium-chain fatty acid and biogas with lignocellulosic raw materials. A method for co-producing medium-chain fatty acids and biogas from lignocellulosic raw materials, comprising the following steps: (1) mixing pulverized lignocellulosic raw materials with an alkaline solution for pretreatment, and subjecting the pretreated mixture to solid-liquid separation; Obtain hydrolyzed liquid and solid residue; (2) mix hydrolyzed liquid with anaerobic digestion sludge, adjust pH to 5.0-5.5, continue anaerobic fermentation, add ethanol or lactic acid in the fermentation process, respectively obtain medium chain fatty acid and post-extraction fermentation (3) Mix the solid residue obtained in step (1) with the extracted fermentation liquid obtained in step (2), and continue anaerobic fermentation for 20-50 days to obtain biogas. Aiming at the characteristics of alkali pretreatment and anaerobic fermentation of lignocellulosic raw materials, the invention establishes a method for co-producing biogas and medium-chain fatty acids, and realizes the cascade utilization of lignocellulosic raw materials.

Description

A method for co-producing medium-chain fatty acids and biogas from lignocellulosic raw materials

Technical field:

The invention relates to the technical field of waste recycling, in particular to a method for co-producing medium-chain fatty acids and biogas from lignocellulosic raw materials.

Background technique:

Lignocellulosic raw materials such as straws and energy herbs are the most abundant and sustainable hydrocarbon biomass resources on the earth, with the characteristics of wide source, large output and stable composition. With the continuous development of biomass energy, the conversion of lignocellulosic raw materials such as straw and energy plants to prepare energy or bio-based products has received more and more attention. It plays an important role in alleviating the pressure on the ecological environment and improving the energy structure.

The main components of lignocellulosic raw materials are cellulose, hemicellulose and lignin, of which cellulose and hemicellulose account for about 66% to 75% and are the main available components. However, due to the close cross-linking of three elements in lignocellulosic raw materials, its special structure, the protective effect of lignin, and the crystallization of cellulose all hinder the hydrolysis of lignocellulosic raw materials and affect the utilization efficiency. Therefore, pretreatment of lignocellulosic raw materials is required to increase the hydrolysis efficiency of the raw materials, thereby improving the conversion rate. Among them, alkali treatment has proved to be very suitable as a pretreatment process for anaerobic fermentation of lignocellulosic raw materials. After pretreatment, the hydrolyzate is mostly hemicellulose hydrolyzate, while the solid residue is mainly cellulose, and the components of each product are different. , with the potential for hierarchical utilization.

Anaerobic fermentation technology is one of the most potential lignocellulosic biomass resource utilization technologies. At present, the technology of producing biogas by anaerobic fermentation of lignocellulosic raw materials has been rapidly developed in my country, and related bioenergy projects have also been accelerated, but there are still problems such as long fermentation cycle, low conversion efficiency, and insufficient product value. In recent years, in addition to using anaerobic technology to prepare biogas, in view of the characteristics and limitations of anaerobic digestion, the international anaerobic field has also proposed a new idea of anaerobic fermentation to prepare volatile fatty acids (VFAs). Promising high-value utilization approach. Among them, medium-chain carboxylic acids such as caproic acid have become one of the most potential platform compounds due to their high energy density, strong hydrophobicity, high added value, and relatively easy subsequent separation and purification.

Invention content:

The object of the present invention is to provide a method for co-producing medium-chain fatty acids and biogas from lignocellulosic raw materials. The present invention aims at the characteristics of alkaline pretreatment and anaerobic fermentation of lignocellulosic raw materials, and establishes a method for co-producing biogas and medium-chain fatty acids. The method realizes the cascade utilization of lignocellulosic raw materials.

The object of the present invention is to provide a kind of method for co-production of medium chain fatty acid and biogas from lignocellulosic raw material, comprising the steps:

(1) Mix the pulverized lignocellulosic raw material with the alkaline solution at a solid-liquid ratio of 1:10 to 1:40, set the temperature to 30 to 80°C, and perform pretreatment for 12 to 48 hours, and the pretreated mixture is solidified. Liquid separation to obtain hydrolyzate and solid residue respectively, and the hydrolyzate is rich in organic substances such as xylan, xylose, glycolic acid, acetic acid;

(2) mixing the hydrolyzate obtained in the step (1) with the anaerobic digestion sludge, adjusting the pH to 5.0～5.5, and continuing to maintain the anaerobic fermentation for 15～30 days, the fermentation temperature is 25～35 ℃, adding in the fermentation process Ethanol or lactic acid, obtain a fermentation broth containing medium-chain fatty acids, extract the medium-chain fatty acids therein, and obtain the medium-chain fatty acids and the fermentation broth after extraction respectively;

(3) The solid residue obtained in step (1) is mixed with the extracted fermentation liquid obtained in step (2), and anaerobic fermentation is continued for 20 to 50 days to obtain biogas.

Preferably, the mass fraction of the alkaline substance in the alkaline solution described in step (1) is 2% to 8%, and the alkaline substance is selected from the group consisting of sodium hydroxide, calcium hydroxide, potassium hydroxide and ammonia water or several.

Preferably, the anaerobic digestion sludge described in step (2) can be derived from the fermentation broth obtained from the anaerobic fermentation project in normal operation, or from the fermentation broth after gas production by anaerobic fermentation in step (3).

Preferably, the amount of ethanol or lactic acid added in step (2) is to add 1.5 to 3 g of ethanol or lactic acid per 100 g of fermentation broth, the ethanol or lactic acid addition interval is 8 to 20 days, and the number of additions is 2 ~ 4 times.

Preferably, the medium chain fatty acid in step (2) is caproic acid or caprylic acid.

Preferably, the solid-to-liquid ratio of the solid residue described in step (3) to the fermentation broth after extraction is 0.03-0.15 g/mL.

Preferably, the lignocellulosic raw material is crop straw or energy grass.

Unless otherwise specified, the definitions of terms involved in the present invention have the same meanings as commonly understood by those skilled in the art.

Compared with the prior art, the present invention has the following advantages:

(1) The present invention utilizes an alkali treatment method to roughly divide the lignocellulosic raw materials into cellulose-based solid residues and hemicellulose hydrolyzate-based hydrolyzed liquids, and for different properties of the products, biogas production and medium-chain fatty acids are carried out respectively. It realizes the classification and utilization of lignocellulosic raw materials.

(2) The present invention realizes the co-production of biogas and medium-chain fatty acids, and increases product types and added value compared with the traditional anaerobic fermentation process; the fermentation broth after acid extraction and the pretreated solid residues produce gas anaerobic together, The active ingredients are used twice, which increases the conversion efficiency of raw materials.

(3) The present invention adopts the biological method to prepare clean energy biogas and carboxylic acid platform compounds such as caproic acid, which can not only realize energy and resource utilization of organic wastes such as straw, but also use petrochemical raw materials to prepare such products. It is a green and clean process to co-generate energy and high value-added platform compounds while waiting for organic waste.

Description of drawings:

1 is a schematic process flow diagram of a method for co-producing medium-chain fatty acids and biogas from lignocellulosic raw materials according to the present invention.

Detailed ways:

The following examples are further illustrations of the present invention, rather than limitations of the present invention. Anaerobic digested sludge is commercially available.

Example 1:

As shown in Figure 1, the method for co-producing caproic acid and biogas by anaerobic fermentation of hybrid Pennisetum comprises the following steps:

(1) pulverize the fresh hybrid Pennisetum to below 1cm, add the sodium hydroxide solution with a mass fraction of 2% by the amount of 40mL/g of the Fresh Hybrid Pennisetum, add sodium hydroxide solution, set the temperature to 30°C, The reaction is pretreated for 48 hours, and the pretreated mixture is subjected to solid-liquid separation to obtain pretreated hydrolyzate and solid residue respectively;

(2) mixing the pretreated hydrolyzate obtained in the step (1) with the anaerobic digestion sludge, adjusting the pH to 5.5 with hydrochloric acid or sulfuric acid and continuing to maintain the anaerobic fermentation for 30 days, the fermentation temperature is 25° C. On the 8th day, the 16th day and the 24th day, ethanol was added, and the amount of ethanol added each time was 1.5 g of ethanol per 100 g of fermentation broth to obtain a fermentation with a caproic acid concentration of 5 g/L and an octanoic acid concentration of 1 g/L. The fermented liquid of the liquid, using the extraction method to extract the caproic acid therein, to obtain the caproic acid and the post-extracted fermentation liquid respectively;

(3) mixing the solid residue obtained in the step (1) and the mixture of the extracted fermentation broth in the step (2), the solid-liquid ratio of the solid residue and the extracted fermentation broth is 0.15g/mL, and the anaerobic process is continued. After 50 days of fermentation, biogas with a methane content of 50-60% is obtained.

Example 2:

As shown in Figure 1, the method for co-producing caproic acid and biogas by anaerobic fermentation of corn stover includes the following steps:

(1) Pulverize the corn stalks to less than 2 cm, add 8% potassium hydroxide solution according to the amount of 10 mL/g of fresh hybrid Pennisetum, set the temperature to 80 °C, and perform pretreatment for 12 hours of reaction to complete the pretreatment. The mixture is separated by solid-liquid to obtain pretreated hydrolyzate and solid residue respectively;

(2) mixing the pretreated hydrolyzate obtained in the step (1) with the anaerobic digestion sludge, adjusting the pH to 5.0 with hydrochloric acid or sulfuric acid and continuing to maintain the anaerobic fermentation for 15 days, the fermentation temperature is 35° C. On the 10th day and on the 10th day, ethanol was added, and the addition amount of ethanol was 3 g per 100 g of fermentation broth, and the concentration of hexanoic acid was 6 g/L, and the hexanoic acid and octanoic acid were extracted by extraction method to obtain hexanoic acid, octanoic acid and octanoic acid respectively. Fermentation broth after extraction;

(3) mixing the solid residue obtained in step (1) with the mixture of the post-extracted fermentation broth in step (2), the solid-liquid ratio of the solid residue and post-extracted fermentation broth is 0.03 g/mL, and the anaerobic process is continued. After 20 days of fermentation, biogas with a methane content of 50-60% is obtained.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, Simplification and the like should all be equivalent substitution methods, and are all included in the protection scope of the present invention.

Claims (7)

1. A method for coproducing medium-chain fatty acid and biogas from wood fiber raw materials is characterized by comprising the following steps:

(1) mixing the crushed wood fiber raw material with an alkaline solution in a solid-to-liquid ratio of 1: 10-1: 40, setting the temperature to be 30-80 ℃, carrying out pretreatment for 12-48 hours, and carrying out solid-liquid separation on the pretreated mixture to obtain a hydrolysate and solid residues respectively;

(2) mixing the hydrolysate obtained in the step (1) with anaerobic digestion sludge, adjusting the pH to 5.0-5.5, continuing to perform anaerobic fermentation for 15-30 days at the fermentation temperature of 25-35 ℃, adding ethanol or lactic acid in the fermentation process to obtain fermentation liquor containing medium-chain fatty acids, and extracting the medium-chain fatty acids to respectively obtain the medium-chain fatty acids and the fermentation liquor after extraction;

(3) and (3) mixing the solid residue obtained in the step (1) with the extracted fermentation liquor obtained in the step (2), and continuously performing anaerobic fermentation for 20-50 days to obtain the biogas.

2. The method for coproducing medium-chain fatty acid and biogas from lignocellulosic raw materials as claimed in claim 1, wherein the alkaline solution in the step (1) contains 2-8% by mass of alkaline substances, and the alkaline substances are selected from one or more of sodium hydroxide, calcium hydroxide, potassium hydroxide and ammonia water.

3. The method for coproducing medium-chain fatty acid and biogas from a wood fiber raw material as recited in claim 1, wherein the ethanol or lactic acid is added in an amount of 1.5-3 g per 100g of fermentation broth in step (2), the time interval between the addition of ethanol or lactic acid is 8-20 days, and the number of addition is 2-4.

4. The method for co-producing medium-chain fatty acid and biogas from a lignocellulosic feedstock as claimed in claim 1, wherein the anaerobically digested sludge in step (2) is a fermentation broth obtained from a normally operated anaerobic fermentation process or a fermentation broth after the gas is produced from the anaerobic fermentation in step (3).

5. The method for co-producing medium-chain fatty acid and biogas as defined in claim 1 or 2, wherein the medium-chain fatty acid in step (2) is hexanoic acid or octanoic acid.

6. The method for co-producing medium-chain fatty acid and biogas from lignocellulosic raw material according to claim 1 or 2, wherein the solid-to-liquid ratio of the solid residue to the fermentation broth after extraction in step (3) is 0.03-0.15 g/m L.

7. The method for co-producing medium-chain fatty acids and biogas from lignocellulosic feedstocks according to claim 1 or 2, wherein the biomass is crop straw or energy grass.

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